Fibronectin (Fn) is a large flexible glycoprotein found in blood and other body fluids and in the extracellular matrix. It interacts with numerous macromolecules including several cell-surface receptors (integrins) and mediates the binding of many types of cells to natural and artificial surfaces. Each of the two chains of Fn contains approximately 30 internally homologous motifs or modules of three different types, each encoded by one or two exons. The long range goals of this research are to elucidate the structure and function of each module in Fn, to know which modules are involved in the multiplicity of interactions and which amino acids within those modules participate directly in molecular recognition processes. This will be accomplished by isolating ever smaller fragments by proteolysis or recombinant techniques and characterizing their thermodynamic properties by differential scanning calorimetry and fluorescence methods. In this proposal we aim first to identify each independently folded domain in Fn and to characterize interactions between neighboring domains. Second, we will identify and characterize intramolecular interactions between distal modules and use the results to develop constraints on models of the structure of Fn in solution. Third, we propose to identify the modules that are responsible for the intermolecular self-associations involved in fibril formation and matrix assembly. Finally, we propose to investigate the interaction of FN with fibrin(ogen) and factor XIII. This work will assist efforts to understand the relationship between the exon structure of genes and the domain structure of gene products, information which will be useful to those attempting to bioengineer new multifunctional modular proteins for specific medical applications. The knowledge gained will also lead to a better understanding of the role of Fn in a variety of physiological processes including cancer, embryogenesis, hematopoiesis, wound healing and hemostasis.